The Nigerian government is violating its own laws by keeping a child bride on death row for murdering her husband almost a year after a regional court dismissed the sentence handed down to her, according to a coalition of human rights campaigners.

Maimuna Abdulmumini, 22, accused of burning her husband to death as a teenager, remains in prison today despite the Economic Community of West African States (Ecowas) Court of Justice ruling in June 2014 that the decision by a court in the north of the country to impose the death penalty was a violation of her fundamental rights.

As the one year anniversary of the ruling approaches, Amnesty International has released a strongly worded statement calling on the Nigerian government to curtail forced marriage as a matter of urgency and abolish the death penalty.

“Nigeria has a great deal of work to do to improve its record on human rights, particularly when it comes to the rights of women and girls,” says a spokeswoman for Amnesty International UK.

“The gender gap last year was shocking. According to the UN’s Gender Equality Index, Nigeria featured 152 on the list of 187 countries.

“An immediate way in which the new government can improve the human rights situation is to abolish the death penalty, and do more to stop early and forced marriage taking place.”

Avocats Sans Frontières (ASF), who filed the case with the Ecowas court and has campaigned for Abdulmumini’s release for over a year, add that “it would be unacceptable for Maimuna Abdulmumini to remain on death row”.

Abdulmumini was 13 when her husband, Ibrahim, burned to death in their marital home. For the five months they were married, their relationship was characterised by systemic abuse, according to Abdulmumini’s lawyers. In response to questions posed by the Guardian and asked through her legal team, Abdulmumini herself said that her husband was “violent” to her in the the time they were married and suffered from a mental illness.

After a legal process dragged on for five years, Abdulmumini was convicted of murder and sentenced to death in December 2012. She has been in prison at Katsina state jail ever since, her mental state gradually deteriorating as she shares an already cramped cell with five other condemned women.

“Although our team has been at her side during all the proceeding initiated before the Ecowas Court, one can hardly imagine how frustrating it is for Maimuna Abdulmumini not to see yet the practical impact of the judgement,” explains Angela Uwandu, from ASF Nigeria.

Born and raised in small village in Katsina state, in northern Nigeria, Abdulmumini received a limited formal education in a two-classroom school. Her only lessons were focused on learning the English alphabet and studying Islam, with her subject being Arabic.

When she turned her 13, her parents told her she would be married. In northern Nigeria, where senators marry teenagers, this wasn’t out of the ordinary; 17% of girls in the country are married before the age of 15, according to the charity Girls Not Brides. In the Muslim-dominated part of the country, nearly half of girls are married by the age of 15 and 78% are married by the time they hit 18. All of this is despite child marriage being prohibited under Nigerian law more than a decade ago.

In 2003, the Child Rights Act, raised the minimum age of marriage for girls to 18, but due to the west African country’s complex federalised system, only 24 of Nigeria’s 36 states have passed the legislation.

In the years following her husband’s death and her trial, Abdulmumini remarried and had a child, Habiba.

In a criminal trial in northern Nigeria, Abdulmumini’s age at the time of the crime was not taken into account. This is despite the death sentence being prohibited for under-18s under international law.

Oliver Robertson, the death penalty and alternatives project manager at Penalty Reform International, says “it is recognised worldwide that people must not be sentenced to death for crimes committed before they were 18.”

“This applies in all circumstances, regardless of whether local laws state that girls are considered adult when they marry.”

Mr Robertson suggests that Nigeria is failing to meet it’s obligations under international law in it’s handling of the case.

“The UN Convention on the Rights of the Child, which Nigeria has ratified, is unequivocal about this, stating: ‘Neither capital punishment nor life imprisonment without possibility of release shall be imposed for offences committed by persons below 18 years of age’,” he explains.

“A key reason why the death penalty is banned for offences committed while a child is that children are still developing, and so are more able to reform and change. Killing them prevents any chance of making a better life for themselves, and for their family.

Abdulmumini’s case has so far failed to gain attention in the international media, beyond stories by the Guardian.

This is in contrast to other death penalty cases in Nigeria which have been subject to lengthy campaigns by western NGOs.

Last year, Amnesty campaigned successfully for the release of Thankgod Ebhos, a Nigerian man who spent 19 years on death row and was seconds away from being executed before an intervention by the Ecowas court.

Traumatised by her time in prison and unable to see her young daughter, Abdulmumini is desperate to be free and reconnect with Habiba.

As Robertson argues, states which have signed up to the UN Convention on the Rights of the Child have an obligation to take into account the interests of children of prisoners when deciding on sentences.

“Countries have an obligation under the Convention on the Rights of the Child to consider the best interests of the child in all situations that concern them: the possible execution of a child’s mother undoubtedly passes that test,” he says.

“Children are not bargaining chips used by defendants to gain support or sympathy. They are individuals with their own rights and needs, and these rights and needs must be considered by the court.”